Catheter having multiple arms with electrode and position sensor

ABSTRACT

A catheter for measuring physiological signals in a heart comprises a structure at a distal end of the catheter wherein the structure has a plurality of arms, an electrode fixed to each arm and a device for generating position information located on each arm. The arms are located near the long axis of the catheter during insertion of the catheter within a heart and the arms are spreadable apart and away from the long axis of the catheter when the structure is within the heart.

This application is a continuation of application Ser. No. 09/109,802,filed Jul. 2, 1998, which is a Continuation of International ApplicationNo. PCT/IL 97/00009 filed on Jan. 8, 1997, and claims the benefit ofU.S. application Ser. No. 08/595,365, filed Feb. 1, 1996, now U.S. Pat.No. 5,738,096, U.S. Provisional Application 60/009,769, filed Jan. 11,1996, and U.S. Provisional Application 60/011,721, filed Feb. 15, 1996.

FIELD OF THE INVENTION

The present invention relates generally to medical electrophysiologysystems, and specifically to invasive medical probes that may be used tomap the electrical activity of the heart.

BACKGROUND OF THE INVENTION

Cardiac catheters comprising electrophysiological sensors are known formapping the electrical activity of the heart. Typically the time-varyingelectrical potentials in the endocardium are sensed and recorded as afunction of position inside the heart, and then used to map the localelectrogram or local activation time. Activation time differs from pointto point in the endocardium due to the time required for conduction ofelectrical impulses through the heart muscle. The direction of thiselectrical conduction at any point in the heart is conventionallyrepresented by an activation vector, which is normal to an isoelectricactivation front, both of which may be derived from a map of activationtime. The rate of propagation of the activation front through any pointin the endocardium may be represented as a velocity vector.

Mapping the activation front and conduction fields aids the physician inidentifying and diagnosing abnormalities, such as ventricular and atrialtachycardia and ventricular and atrial fibrillation, that result fromareas of impaired electrical propagation in the heart tissue. Localizeddefects in the heart's conduction of activation signals may beidentified by observing phenomena such as multiple activation fronts,abnormal concentrations of activation vectors, or changes in thevelocity vector or deviation of the vector from normal values.Furthermore, there may be no electrical propagation at all withindefective portions of the heart muscle that have ceased to function, dueto local infarction, for example. Once a defect is located by suchmapping, it may be ablated (if it is functioning abnormally) orotherwise treated so as to restore the normal function of the heartinsofar as is possible.

Mapping of the electrical activation time in the heart muscle requiresthat the location of the sensor within the heart be known at the time ofeach measurement. Such mapping may be performed using a single movableelectrode sensor inside the heart, which sensor measures activation timerelative to a fixed external reference electrode. This technique,however, gives maps of low resolution and relatively poor accuracy,limited by the accuracy of determination of the position of theelectrode at the time of each measurement. The natural movement of theheart makes it very difficult to maintain an accurate reading of theposition of the moving electrode from beat to beat. Mapping ofelectrical activation time using a single electrode is, furthermore, alengthy procedure, which must generally be performed under fluoroscopicimaging, thereby exposing the patient to undesirable ionizing radiation.Further, in an arrhythmic heart, activation times at a single locationmay change between consecutive beats.

Because of these drawbacks of single-electrode mapping, a number ofinventors have taught the use of multiple electrodes to measureelectrical potentials simultaneously at different locations in theendocardium, thereby allowing activation time to be mapped more rapidlyand conveniently, as described, for example, in PCT patent publicationWO 95/05773, whose disclosure is incorporated herein by reference. Inthis case, the positions of all the electrode sensors must be determinedat the time of measurement, typically by means of fluoroscopic orultrasonic imaging. These methods of position determination, however,are complicated, inconvenient and relatively inaccurate, thereforelimiting the accuracy of mapping.

Alternatively, U.S. Pat. Nos. 5,471,982 and 5,465,717, whose disclosuresare incorporated herein by reference, teach the use of an electrodebasket, which is inserted into a chamber of the heart and then expandedso that a plurality of electrodes are simultaneously brought intocontact with multiple points on the endocardium. The relative electricalactivation times at all the electrodes may then be measuredsimultaneously and used to detect and localize abnormalities. The basketis of limited usefulness in creating high-resolution maps of theelectrical activation vector, however, because it cannot easily berepositioned once it is expanded inside the heart, and furthermore,determining the absolute positions of the electrodes requires the use offluoroscopy or other painstaking and undesirable imaging methods.Further, the basket catheter does not contract with the heart, so theelectrodes in the basket catheter cannot maintain contact with the sameportion of the myocardium for the entire cycle, and the electrodes maynot return to the same position relative to the myocardium for eachcycle.

U.S. Pat. No. 5,487,391, to Panescu, for example, describes a multipleelectrode probe for deployment inside the heart. Signals received fromthe multiple electrodes are used for deriving the propagation velocityof depolarization events. This patent makes no provision, however, forindependently determining the positions of the electrodes relative to anexternal or heart-fixed frame of reference, and the velocity is derivedrelative to the probe, rather than to the heart itself.

Detecting the position in space of a single electrophysiology mappingelectrode is described, inter alia, in PCT patent application numberPCT/US95/01103, filed Jan. 24, 1995, U.S. provisional application60/009,769, filed Jan. 11, 1996, U.S. patent application Ser. No.08/595,365, filed Feb. 1, 1996, both titled “Cardiac Electromechanics”,and U.S. Pat. No. 5,391,199, issued Feb. 21, 1995, the disclosures ofall of which are incorporated herein by reference.

U.S. Pat. No. 5,450,846, whose disclosure is incorporated herein byreference, describes a catheter, which may be easily repositioned insidethe heart, comprising an ablator at its distal tip and pairs ofnon-contacting sensing electrodes arrayed around the outside of thecatheter near the distal end. Each electrode senses local electrogramsignals generated in the endocardium in a small area near the side ofthe catheter that it faces. Differences in the activation times in thesignals sensed by the pairs of electrodes are used to estimate thedirection of the activation vector in the vicinity of the catheter, soas to guide the operator in positioning the ablator. However, use ofthis device in high-resolution mapping of activation vectors is notpractical either, because of the difficulty of determining the absoluteposition of the catheter tip, which must be performed by imagingmethods, and because of the inferior accuracy of the non-contactelectrogram measurement.

PCT publication WO/ 95/10226 describes a catheter that includes a ringat its distal end, designed to bear against the circumference of a valveof the heart. The ring comprises electrodes, which measure electricalactivity in the valve tissue. When abnormal electrical activity isdetected in the valve tissue adjacent to one of the electrodes, anelectrical current is applied through the electrode so as to ablate thetissue at the site of the abnormal activity. The invention provides nomeans for determination of the position of the ring and electrodes,however, other than methods of imaging known in the art, and istherefore not useful for mapping electrical activity, nor is it usefulin areas of the heart other than the valves.

U.S. Pat. No. 5,555,883, to Avitall, the disclosure of which isincorporated herein by reference, describes a catheter with a loopshaped mapping and ablation system. There is no provision, in thispatent, for determining the position of individual electrodes relativeto the heart surface being mapped/ablated.

SUMMARY OF THE INVENTION

It is an object of the present invention to allow simultaneousmeasurement of physiological signals by multiple sensors inside a humanbody, while simultaneously providing accurate measurement of at leastthe relative locations of all the sensors.

In one aspect of the invention, the sensors are fixed to a catheter, andthe locations of the sensors arc measured by determining the position ofa device in the catheter that generates position and orientationinformation.

A further object of the present invention is to provide a method and adevice for rapidly and accurately measuring local electrical propagationvectors in the heart muscle, in order to locate sites of abnormalelectrical propagation, for purposes of subsequent diagnosis andtherapy.

In a preferred embodiment of the present invention, a plurality ofelectrodes are attached to a structure at the distal end of a catheter.One or more devices for generating position information are placed inproximity to the electrodes, so that the positions of all the electrodescan be determined in relation to an external frame of reference orrelative to the heart. The position information and signals measured bythe electrodes are used to determine the direction and magnitude of theelectrical activation vector at the location of the structure at thedistal end of the catheter.

In preferred embodiments of the present invention, the structure at thedistal end of the catheter comprises at least three non-collinearelectrodes, so that the direction of the electrical activation vector inthe plane defined by the electrodes may be fully determined.

In some preferred embodiments of the present invention, the electrodesare attached to a substantially rigid ring at the distal end of acatheter. A device that generates position information is coupled to thering, so that the position and rotational orientation of the ring may bedetermined, thus determining the locations of all the electrodes.Alternatively or additionally, the geometrical shape and angularorientation of the ring are known relative to the catheter. If thelocations of the electrodes relative to the catheter are substantiallypredetermined, the positions of all the electrodes may be determinedfrom a determined position and orientation of the catheter tip. Further,in this case, it is sufficient to determine the location of the tip andonly the rotational coordinate of the catheter tip around its axis.

A catheter of the present invention is preferably inserted into achamber of the heart. The ring at the distal end of the catheter isplaced in contact with the endocardium, and the electrical propagationvector is measured at the location of the ring. The distal end of thecatheter may then be repeatedly repositioned to other locations on theendocardium, so as to generate a map of the propagation vector field orto locate an area of abnormality.

In the context of this invention, the term substantially rigid, asapplied to the ring at the distal end of the catheter, is taken to mean,that during successive measurements of electrophysiological signals bythe electrodes, the shape of the ring and its angular orientationrelative to the long axis of the catheter remain fixed in a known,predetermined relation. Consequently, the location of each of theelectrodes on the ring relative to a coordinate information device isfixed and known, and thus the locations of all the electrodes relativeto an external reference frame may be determined using the location andorientation information provided by the coordinate information device.However, in some embodiments of the invention, where individualelectrodes are fixed to the myocardium, such as when using extendiblebarbs to hold the electrodes in place, the electrodes are allowed tomove relative to each other, as a result of myocardial contraction.

Although the substantially rigid ring maintains its shape duringmeasurements, for purposes of insertion and removal of the catheter thering may be straightened or flattened, so as to pass easily throughnarrow channels, such as blood vessels, or through a lumen of thecatheter.

In a preferred embodiment of the present invention, the substantiallyrigid ring is formed of a resilient, super-elastic material, such asNiTi. For insertion or removal of the catheter from the body, the ringis compressed inside a narrow sleeve adjacent to the distal end of thecatheter. After insertion of the catheter, the ring is ejected from thesleeve and assumes its predetermined shape and position.

In one preferred embodiment of the invention, the substantially rigidring is made from a flat, ribbon-like section of resilient material. Thedistal end of the catheter, with which the ring is in contact after ithas been ejected from the sleeve, is likewise flat and includes a slotnecessary for ejection of the ring. Thus once the ring is ejected, it issubstantially prevented from rotating or tilting relative to the axis ofthe catheter and does not substantially bend or deform under the forcesexerted on it during successive measurements inside the heart. In thismanner the positions of the electrodes on the ring are maintained inpredetermined relations to the distal end of the catheter.

In another preferred embodiment of the present invention, the ring isformed of a hollow section of resilient, superelastic material, which isrigidly coupled to the distal end of the catheter at a known angularorientation. For insertion or removal of the catheter from the body, thering is straightened by insertion of a stylette into the lumen of thehollow section. After insertion of the catheter into the heart, thestylette is withdrawn, and the ring reassumes its predetermined shapeand orientation.

In an alternative preferred embodiment of the present invention, thering at the distal end of the catheter is formed of a hollow section offlexible material, which is straightened for insertion or removal of thecatheter from the body by insertion of a straight stylette into thelumen of the hollow section. After the straight stylette is withdrawn, asecond stylette, formed of substantially rigid, resilient material andincluding a curved portion at its distal end, is inserted. For insertionof this second stylette through a lumen of the catheter, the curveddistal portion of the stylette is straightened, and the relativestiffness of the catheter causes the stylette to remain straight. Whenthis stylette reaches the hollow, flexible section at the distal end ofthe catheter, however, the resilience of the stylette causes its distalportion to resume its curved shape, and thus causes the hollow, flexiblesection of the catheter to curve, as well, into the desired ring shape.

In some preferred embodiments of the present invention in which thedistal end of the catheter is straightened during insertion into theheart, when the section at the distal end of the catheter is caused tocurve into a ring shape after insertion, the distal tip of this sectionengages a socket in the side of the catheter. Fluoroscopy or othermethods of imaging known in the art may be used to observe the ring atthe distal end of the catheter and verify that the distal tip of thedistal section has engaged the socket, so as to ensure that the ring hasassumed its desired shape and orientation prior to beginningelectrophysiological measurements.

Alternatively, in some preferred embodiments of this type, the distaltip of the distal end section of the catheter comprises a firstelectrical contact, and the socket in the side of the catheter comprisesa second electrical contact. When the distal tip engages the socket, thefirst electrical contact is brought into proximity with the secondelectrical contact. The mutual proximity of the contacts is measuredelectrically using methods known in the art, so as to verify that thedistal tip has engaged the socket.

In other preferred embodiments of the present invention, the structureto which the electrodes are attached at the distal end of the cathetermay comprise a ring of any desired cross-sectional profile, or thestructure may be formed in a shape of non-uniform profile. In one suchpreferred embodiment, the structure comprises rigid sections, to whichthe electrodes are attached, and flexible, resilient sections betweenthe rigid sections. The flexible, resilient sections allow the structureto be easily collapsed for passage through the blood vessels, and thencause the structure to resume its desired shape for making measurementswhen released inside a chamber of the heart.

In still other preferred embodiments of the present invention, thestructure to which the electrodes are attached at the distal end of thecatheter is polygonal, most preferably triangular with sharp vertices.When the sharp vertices of the polygonal structure are brought intocontact with the endocardium, they will typically lodge in smallcrevices in the heart tissue, thus preventing the structure from movingduring measurement, despite the natural motion of the heart. Theelectrodes are preferably at the vertices.

In other preferred embodiments of the present invention, the structurein which the electrodes are placed at the distal end of the cathetercomprises multiple arms, wherein electrodes are fixed to the arms.During insertion of the catheter into the heart, the arms are heldparallel and adjacent to the long central axis of the catheter. Onceinside the heart, the arms spread apart, away from the long axis of thecatheter at predetermined, known angles.

In one such embodiment of the present invention, each arm is formed ofat least two sections of substantially rigid material, connectedtogether by a resilient joint. The arms are joined at their proximalends to the distal end of the catheter. A draw-wire passes through alumen in the catheter and is attached at its distal end to the distalends of the arms, which are joined together. During insertion of thecatheter into the heart, the resilient joints tend to hold the armsstraight and parallel to the long central axis of the catheter. Once thearms are wholly inside the heart, the draw-wire is pulled back towardthe proximal end of the catheter, thereby drawing in the distal ends ofthe arms and causing the arms to flex at their resilient joints. Thedraw-wire is pulled back until the joints are completely flexed, and thedistal ends of the arms are brought into close proximity with theproximal ends thereof, so that the arms protrude laterally out from thelong central axis of the catheter. For removal of the catheter from theheart, the draw-wire is released, and the resilient joints straighten totheir original shapes.

In another such embodiment of the present invention, substantially rigidarms, having electrodes adjacent to their distal ends, are containedinside a lumen of the catheter during insertion of the catheter into theheart. Once the distal end of the catheter has been inserted into theheart, the distal ends of the arms are ejected through small radialopenings, spaced around the axis of the catheter. The resilience of thearms causes them to spread apart radially away from the long centralaxis of the catheter and axially, distal to the distal end of thecatheter.

In yet other preferred embodiments of the invention, the structure atthe distal end of the catheter is a balloon or another inflatablestructure, to which electrodes are fixed. After the catheter has beeninserted into the heart, the structure is inflated and assumes apredetermined, known shape and orientation relative to the distal end ofthe catheter.

In some preferred embodiments in accordance with the present invention,the device that generates position information comprises a plurality ofcoils, as disclosed in PCT patent application number PCT/US95/01103,filed Jan. 24, 1995, which is assigned to the assignee of the presentapplication and whose disclosure is incorporated herein by reference.This device continuously generates six-dimensional position andorientation information regarding the catheter tip. This system uses aplurality of non-concentric coils adjacent to a locatable site in thecatheter, for example near its distal end. These coils generate signalsin response to externally applied magnetic fields, which allow for thecomputation of six location and orientation coordinates, so that thelocation and orientation of the catheter in the heart are known withoutthe need for simultaneous imaging, by fluoroscopy or ultrasound, forexample. This device generates position information relative to areference frame defined by field generator coils. In a preferredembodiment of the invention, a Carto system, available from BiosenseLTD., Tirat Hacarmel, Israel, is used for determining the position of acatheter.

Other preferred embodiments of the present invention comprise one ormore devices for generating three-dimensional location information, asdescribed, for example, in U.S. Pat. No. 5,391,199, to Ben-Haim, and PCTpatent application PCT/US94/08352, which are assigned to the assignee ofthe present application and whose disclosures are incorporated herein byreference. One or more devices for generating location information areplaced in the catheter or in the structure containing the electrodes, inproximity to the electrodes. Location information generated by thesedevices is used to determine the positions of the electrodes.

In one such preferred embodiment of the present invention, two or moredevices for generating three-dimensional location information are placedin known, mutually-spaced locations in the catheter or in the structurecontaining the electrodes, thereby allowing the positions of theelectrodes in the structure to be determined.

The device disclosed in the aforementioned '539 patent application forgenerating three-dimensional location information preferably comprises asingle coil. In preferred embodiments of the present invention thatinclude a device of this type, the coil is toroidal in shape and coaxialwith the long, central axis of the catheter. These embodiments thus havethe advantage that the catheter may have one or more lumens, which passthrough the opening at the center of the toroidal coil, whilemaintaining a relatively small external catheter diameter.

In some preferred embodiments of the present invention, a device, suchas described above, for generating three-dimensional locationinformation is placed in the catheter adjacent to the electrodes and isused to determine the location of the catheter inside the heart. One ormore rotation measuring devices measure the angular orientation of thedistal end of the catheter. Since the structure in which the electrodesare placed allows the positions and orientations of the electrodes to beknown relative to the distal end of the catheter, the locationinformation generated by the location generating device in the catheter,taken together with the measured angular orientation of the catheter, issufficient to fully determine the locations of the electrodes in theheart.

The rotation measuring device of this embodiment may be of any suitabletype known in the art. For example, shaft encoder devices adjacent tothe proximal end of the catheter may be used to measure the angle ofrotation of the catheter about its long central axis and/or the angle ofdeflection of the catheter's distal tip. This embodiment of theinvention is especially useful when the path of the catheter isrelatively straight.

In some preferred embodiments of the present invention, used for mappingthe electrical activity of the heart, two catheters are inserted intothe heart. A first catheter comprises a ring with electrodes and adevice that generates position information, as described above. A secondcatheter comprises a device that generates position information, and ispositioned in a predetermined location in a chamber of the heart,preferably at the apex of the heart. This second catheter thus allows areference frame to be defined that is substantially fixed with respectto the heart, relative to which the position of the first catheter isdetermined, so that errors in position determination due to motion ofthe heart and the chest, due to breathing, for example, may be canceled.

In a preferred embodiment of the present invention, for use indiagnosing and treating defects in the heart's electrical conduction,the distal end of the catheter is placed in proximity to the suspectedsite of a defect. On the basis of the vector direction and magnitude ofthe electrical impulse flow vector measured at this initial site, thecatheter is then moved toward the suspected defect. This procedure isrepeated until the catheter reaches the site of the defect. Preferablyonce the defect is located by the above procedure, it is ablated orotherwise treated by methods known in the art.

While the above preferred embodiments have been described with referenceto measurement of electrophysiological signals in the heart, otherpreferred embodiments of the present invention may be used to measureand map electrical signals in the brain or in other physiologicalstructures.

Furthermore, in other preferred embodiments of the present invention,other sensors, such as ionic sensors, may be used instead of theelectrodes to perform localized measurements and map other aspects ofphysiological activity.

It is another object of some embodiments of the present invention toprovide a method for accurately and rapidly determining the magnitudeand direction of a vector corresponding to the propagation of activityin physiological tissue.

In one aspect of the present invention, the activity is electricalactivity in the heart of a subject, and the vector corresponds to thelocal velocity of an electrical activation signal. In other aspects ofthe present invention, the vector corresponds to an ionic current causedby repolarization of the heart tissue, or to currents associated withother elements of the cardiac cycle.

In other aspects of the present invention, the activity is ionicactivity or mechanical activity, such as contraction of muscle tissue,and the vector corresponds to the local ionic or isotonic current,respectively.

In a further aspect of the present invention, the magnitude anddirection of the vector are determined at a plurality of knownlocations, and are used to generate a map of the vector as a function oflocation and/or as a function of time.

In preferred embodiments of the present invention, a plurality ofelectrodes are placed in known positions adjacent to a location in theendocardium. Electrical signals received from the plurality ofelectrodes are used to determine local activation times at therespective positions thereof. A local velocity vector is then calculatedby comparison of the relative values of the local activation time at thepositions of the electrodes.

In preferred embodiments of the present invention, the plurality ofelectrodes comprises at least three electrodes. The local velocityvector is determined by finding velocity vector components along twonon-parallel axes, wherein each of the axes is defined by a pair of theelectrodes. Vector arithmetic operations are applied to the velocityvector components to find the direction and magnitude of the localvelocity vector.

In preferred embodiments of the present invention, the velocity vectorcomponent along each of the axes defined by a pair of electrodes isfound by dividing the distance between the electrodes by the differencein their activation times. However, if the difference in activationtimes between a first pair of electrodes is substantially zero, whilethe difference in activation times between a second pair of electrodesis not zero, then the local velocity vector is found to be perpendicularto the axis defined by the first pair of electrodes. If all theelectrodes have substantially the same activation time, then the localvelocity vector is found to be zero, and the location in the endocardiumto which the electrodes are adjacent is determined to contain asuspected site of pathology, for example, a sink or source of localelectrical activation.

In preferred embodiments of the present invention, the local velocityvector is mapped at a plurality of locations in the heart by placing theelectrodes at the plurality of locations in succession, and determiningthe local velocity vector at each location. Preferably the mapping ofthe local velocity vector is used to determine locations of defects inthe propagation of electrical activation in the endocardium, andparticularly to find sources and sinks of the activation.

Although preferred embodiments of the present invention are describedwith reference to certain types of catheter and position-sensingapparatus, it will be understood that the inventive principles of thepresent invention will be equally applicable to other types of probesand to other apparatus and methods, such as ultrasound or fluoroscopicimaging, for determining the positions of sensors attached to theprobes.

Alternatively, the inventive principles of the present invention may beapplied to measure a local velocity vector without determining thepositions or orientations of sensors used in the measurement relative toan external frame of reference. This measurement is useful, for example,in identifying local conduction defects. On the basis of the vectordirection of the electrical impulse flow vector measured at an initialsite, the catheter is then moved toward the suspected defect. Thisprocedure is repeated until the catheter reaches the site of the defect.Preferably once the defect is located by the above procedure, it isablated or otherwise treated by methods known in the art.

It will further be understood that although preferred embodiments of thepresent invention are described with reference to measurement andmapping of electrical activation in the endocardium, the inventiveprinciples of the present invention will be equally applicable tomeasurement and mapping of the propagation of other signals in theheart, such as isotonic currents and injury currents, as are known inthe art. Similarly, these inventive principles may be applied tomeasurement and mapping of other physiological signals, such as thosearising from electrical activity in the brain, or signals received fromionic sensors.

Another aspect of the present invention relates to a soft tip catheter,which may be safely and easily inserted into a body vessel. Thiscatheter of the present invention preferably includes a resilient capmember extending distally from a distal end of the catheter. Theresilient cap member preferably includes a tuft of at least one distallyextending, resilient lobe with a soft, smooth outer surface or surfaces,preferably constructed of an elastomeric material, such as rubber, latexor silicon-rubber. The cap may be an attachment to the catheter or maybe formed as an extension of the catheter material.

Preferably at least one sensor is fixed to the resilient cap member,preferably at the at least one lobe. The sensors may be any type ofsensor useful in sensing a physiological activity, for example,determining location and orientation of a tumor, or determining properfunctioning of a heart, such as contraction time of a heart muscle, orsensing an activation signal of a heart muscle. Preferably, each lobealso includes apparatus for fixing the lobe to the myocardium, forexample, an extendible barb, a lumen attached to an external vacuumpump, or a bump in the external surface of the lobe and which engageslocal irregularities in the heart muscle.

As the catheter is inserted into a body vessel in a distal direction,the resilient cap member and its lobes may be resiliently inverted overthe distal end of the catheter. The resilient inversion of resilient capmember greatly facilitates insertion of the catheter into the vessel,and provides a high degree of insertion safety, thereby substantiallyeliminating the possibility of the catheter scraping an inner surface ofthe vessel. The cap and lobes may also be inverted by if they collidewith an obstruction as a result of the distal movement of the catheter.The resilient cap member also substantially prevents accidentallypuncturing, scraping or otherwise damaging the interior surfaces of abody organ.

In a preferred embodiment of the invention, the catheter includes aposition sensor at the base of the tuft, for determining the position ofthe catheter tip. Preferably, each of the sensors on the tufts has aknown position relative to the position sensor. Thus, if the positionsensor provides both position and orientation information, the relativepositions of all the sensors can be determined. In a preferredembodiment of the invention, the tufts are arranged so that smallchanges in the positions of the tuft relative to the base (for example,as a result of forward pressure) do not substantially change therelative positions of the tufts.

In a preferred embodiment of the invention, there are no sharp comers orcrevasses between the tufts, so that no blood can collect and clotthere.

There is therefore provided, in accordance with a preferred embodimentof the present invention, elongate probe apparatus for insertion intothe body of a subject, including a structure having a substantiallyrigid configuration; a plurality of physiological sensors, whichgenerate signals responsive to a physiological activity, the sensorshaving substantially fixed positions on the structure in thesubstantially rigid configuration; and one or more devices that generateposition signals indicative of the positions of the physiologicalsensors on the structure in the substantially rigid configuration.

Preferably, the elongate probe comprises a distal end, which is insertedinto the body of the subject, wherein the structure, which preferably ismade of resilient material, or more preferably superelastic material,has a known shape and orientation in its substantially rigidconfiguration relative to the distal end of the probe.

Preferably the structure has the shape of a ring in its substantiallyrigid configuration, and the sensors are mutually spaced around thecircumference of the ring. The structure may be made of a flat strip,formed into a ring.

Alternatively, the structure may include a hollow tube. Preferably thetube is formed of flexible material, and the structure further includesa curved stylette, insertable into the center of the hollow tube so asto cause the hollow tube to assume a curved shape.

Alternatively, the structure may have a polygonal shape, preferablytriangular, in its substantially rigid configuration. Preferably thesensors are adjacent to the vertices of the structure in itssubstantially rigid configuration.

In other preferred embodiments of the present invention, the structureincludes a multiplicity of arms, such that when the structure is in itssubstantially rigid configuration, the arms spread radially outwardrelative to an axis parallel to the long dimension of the elongateprobe.

Preferably the arms include substantially rigid segments, which arecoupled by resilient joints. Flexure of the joints causes the arms tospread radially outward in the substantially rigid configuration of thestructure

Alternatively, the elongate probe includes mutually spaced radialopenings in its outer surface, and the arms protrude from the probethrough the openings.

In other preferred embodiments of the present invention, the structurefurther includes an inflatable element, preferably a balloon. Inflationof the inflatable element causes the structure to assume a substantiallyrigid configuration. Preferably the structure further includes flexible,non-extensible wires.

Preferred embodiments of the present invention further provide that whenthe structure is in its substantially rigid configuration, the positionsof the sensors on the structure define a plane, with a first axisperpendicular to this plane; and the elongate probe defines a secondaxis parallel to its long dimension. The first axis may preferably besubstantially parallel to the second axis, or substantiallyperpendicular to it.

In some preferred embodiments of the present invention, the structurehas a second configuration, in which the structure is relatively narrowand elongated. Preferably, the structure in its narrow, elongatedconfiguration has a long axis that is substantially parallel to an axisdefined by the long dimension of the elongate probe.

In preferred embodiments of the present invention in which thestructure, in its substantially rigid configuration, has the shape of aring, the elongate probe may preferably include an external sheath,defining a central cavity, and the ring is preferably constructed so asto be withdrawn into the central cavity and thus compressed into anarrow, elongated configuration.

In preferred embodiments of the present invention in which the structureincludes a hollow tube, a straight stylette is preferably provided forinsertion into the center of the hollow tube, so as to cause the hollowtube to assume a straight shape. Preferably the structure includes adistal tip, and the elongate probe includes a socket in its side, sothat the distal tip of the structure engages the socket when thestructure assumes its substantially rigid, ring-shaped configuration.More preferably, the distal tip of the structure includes a firstelectrical contact, and the socket in the side of the catheter includesa second electrical contact; and contact between the first and secondelectrical contacts is measured so as to verify that the distal tip hasengaged the socket.

In preferred embodiments of the present invention that include arms madeup of substantially rigid segments and flexible joints, straighteningthe joints preferably causes the segments to maintain a substantiallyparallel alignment with an axis parallel to the long dimension of theelongate probe.

In preferred embodiments of the present invention in which the structureincludes arms that protrude from the elongate probe through openings inits outer surface, the probe preferably further includes one or morelumens, and the structure has a second configuration in which the armsare held inside the one or more lumens.

Preferred embodiments of the present invention further provide that atleast one of the one or more position signal generating devices is fixedin a known relation to the position of the structure in itssubstantially rigid configuration. Preferably at least one of the one ormore position signal generating devices is fixed to the distal end ofthe elongate probe.

Preferably the position signal generating device comprises one or morecoils, which generate position signals in response to an externallyapplied magnetic field. Preferably at least one of the coils is coaxialwith an axis defined by the long dimension of the elongate probe.

Preferably at least one of the one or more position signal generatingdevices generates six-dimensional position and orientation information.Alternatively, the one or more position signal generating devicesinclude, at least two devices for generating three-dimensional locationinformation, placed in a mutually spaced relation. One of the one ormore position information generating devices may be associated with eachof the sensors.

Alternatively, the one or more position signal generating devices mayinclude at least one device that generates three-dimensional locationsignals, and at least one device that generates angular orientationsignals. Preferably, the at least one device that generates angularorientation signals is a rotation measuring device. This rotationmeasuring device may generates information regarding the rotation of thecatheter about an axis defined by the catheter's long dimension.Alternatively or additionally, the device may generate informationregarding deflection of the distal end of the catheter.

Preferred embodiments of the present invention provide that the sensorsbe adapted to detect electrical impulses in the endocardium, where,preferably, the sensors are electrodes adapted to be placed in contactwith the endocardium.

Alternatively, the sensors may be adapted to detect electrical signalsin the brain, or the sensors may be ionic sensors.

Preferred embodiments of the present invention further include signalprocessing circuitry, which receives and processes position signals fromthe probe, so as to determine the positions of the physiologicalsensors. This signal processing circuitry is preferably further oralternatively adapted to measure a vector relating to the physiologicalactivity.

There is further provided in accordance with a preferred embodiment ofthe present invention, apparatus for measuring physiological activity,including an elongate probe for insertion into the body of a subject,which probe includes a plurality of physiological sensors, whichgenerate signals responsive to the physiological activity; and signalprocessing circuitry, which receives and processes physiological signalsfrom the probe, so as to measure a vector relating to the physiologicalactivity.

In accordance with a further preferred embodiment of the presentinvention, there is provided apparatus for measuring physiologicalactivity including elongate probe apparatus adapted to detect electricalimpulses in the endocardium, as described above, and further includingsignal processing circuitry, which measures an electrical activationvector in the heart.

Furthermore, in accordance with other preferred embodiments of thepresent invention, there is provided apparatus including a firstelongate probe adapted to detect electrical impulses in the endocardium,as described above; and a second elongate probe, having a distal end,which is inserted into a human body, and a device that generatesposition signals indicative of the three-dimensional location of thedistal end of the second probe. Preferably, the second elongate probe isadapted to be substantially fixed in a chamber of the heart, and theposition signals generated by the device indicative of the location ofthe distal end of the second probe define a reference frame relative towhich the position and orientation of the structure of the firstelongate probe are determined. Preferably the second probe is adapted tobe substantially fixed adjacent to the apex of the heart.

There is further provided in accordance with a preferred embodiment ofthe present invention, a method for mapping electrical activity in theendocardium of a heart, including:

inserting a catheter, having a distal end, to which a structure having asubstantially rigid configuration is connected, and to which structure aplurality of sensors are fixed in known positions, into a chamber of theheart, so as to bring the sensors into contact with a locus in theendocardium;

receiving electrical signals indicative of electrical activity in theendocardium at the plurality of sensors;

determining the respective position of the sensors using positioninformation generated by one or more position information generatingdevices fixed in known relation to the sensors.

Moreover, there is provided in accordance with another preferredembodiment of the present invention, a method for mapping electricalactivity in the endocardium of a heart, including:

inserting a first catheter, having a distal end, to which a structurehaving a substantially rigid configuration is connected, and to whichstructure a plurality of sensors are fixed in known positions, into achamber of the heart, so as to bring the sensors into contact with alocus in the endocardium;

inserting a second catheter, having a distal end, to which a device thatgenerates three-dimensional location information is connected, into achamber of the heart, so as to fix the distal end of the second catheterin a known, predetermined position in the chamber of the heart;

receiving electrical signals indicative of electrical activity in theendocardium at the plurality of sensors;

determining the respective positions of the sensors relative to areference frame defined by the second catheter, using positioninformation generated by one or more position information generatingdevices fixed in known relation to the sensors.

Preferably, in either of the above methods, the structure is insertedinto a chamber of the heart by passing the structure through a bloodvessel, and during insertion, the structure assumes a secondconfiguration, which is narrow and elongated so as to pass easilythrough the blood vessel.

Preferably the electrical signals and the position information inaccordance with the above methods are used to determine an activationvector at the locus. Preferably the vector is determined by measuringactivation times of the electrical signals.

Furthermore, the one or more devices for generating position informationpreferably measure the position and orientation of the structure.

Preferred embodiments of the present invention provide that the sensorsare coupled together as bipolar electrodes, and the vector is determinedby measuring amplitudes of electrical signals received from the bipolarelectrodes.

Preferred embodiments of the present invention further provide that theactivation vector is mapped by receiving electrical signals from theendocardium and determining the respective positions of the sensors atmultiple loci in the heart. Preferably the location of a defect in theheart's electrical conduction is determined by measuring the directionof propagation of electrical impulses in the heart repeatedly atmultiple locations.

There is further provided, in accordance with a preferred embodiment ofthe invention a catheter insertable into a body vessel comprising: atubular body portion; at least one resilient member extending from adistal end of said tubular body portion, said at least one resilientmember being adapted to bend over the outside of the distal end of thetubular portion and to extend distally from the distal end of thetubular portion.

Preferably, the at least one resilient member is adapted to bend overthe outside of the distal end of the tubular portion during distalmotion of the catheter in a vessel and is adapted to extend distallyfrom the distal end of the tubular portion during proximal motion of thecatheter in the vessel.

In a preferred embodiment of the invention the at least one resilientmember has a rest position at which it does not extend axially from thetubular section.

In a preferred embodiment of the invention, the at least one resilientmember comprises a plurality of resilient members attached to the distalend of the tubular section.

Preferably the plurality of resilient members are substantiallysymmetrically arranged about a longitudinal axis of said catheter.

In a preferred embodiment of the invention the at least one resilientmember is comprised in a cap attached to the distal end of the tubularmember. Preferably, the cap comprises a sleeve extending from a proximalend of said resilient member and attachable to said distal end of saidtubular body portion, wherein at least one radial dimple is formed at ajuncture between said sleeve and said resilient member.

In a preferred embodiment of the invention the at least one resilientmember is constructed of an elastomeric material.

Preferably the catheter comprises at least one bump protruding from saidat least one resilient member, preferably having at least one sensorfixed to said bump.

Preferably the catheter comprises at least one sensor fixed to said atleast one resilient member.

In preferred embodiments of the invention the at least one sensor isselected from the group consisting of a position sensor, a six degree offreedom position and orientation sensor, a monopolar electrode, abipolar electrode, a strain gauge and a physiological activity sensor.

There is further provided, in accordance with a preferred embodiment ofthe invention, a method for sensing a physiological activity of tissueinside a body organ, comprising:

inserting a catheter having at least according to any of claims 72-74into said body organ;

sensing a physiological activity of said tissue with each sensor.

Preferably the sensors sense a physiological activity substantiallysimultaneously.

In preferred embodiments of the invention the physiological activity isselected from the group consisting of movement of said tissue,contraction time of a heart muscle, an activation signal of a heartmuscle, and velocity of fluid flow.

There is further provided, in accordance with a preferred embodiment ofthe invention, a method for determining a velocity relating tophysiological activity at a location in a tissue, comprising:

receiving signals indicative of physiological activity at a plurality ofknown positions adjacent to the location in the physiological tissue;

measuring a respective characteristic time at each of the plurality ofpositions using the signals received therefrom;

computing velocity component vectors along two non-parallel axes,wherein the velocity component vectors are defined by the knownpositions and the measured activation times; and

applying vector arithmetic operations to the velocity component vectorsto determine the velocity at the location.

In a preferred embodiment of the invention each of the two non-parallelaxes is defined by a respective pair of the known positions. Preferablyeach of the velocity component vectors has a magnitude determined byarithmetically dividing the distance separating the pair of knownpositions that define the respective axis of the velocity componentvector, by the difference of the characteristic times between the knownpositions.

In a preferred embodiment of the invention and including finding one ofthe plurality of positions that has a characteristic time notsubstantially equal to the characteristic times of the other positions.Preferably the method comprises taking the position whose characteristictime is not substantially equal to the characteristic times of the otherpositions as a reference point for computing the velocity componentvectors. Preferably, both of the non-parallel axes are taken to passthrough the reference point.

In a preferred embodiment of the invention the method includes thelocation as a possible site of pathology when all of the plurality ofpositions are found to have a substantially equal characteristic times.

Preferably, the method includes determining the coordinates of thelocation relative to an external frame of reference.

In a preferred embodiment of the invention, where the signals areelectrical signals, which are received by a plurality of electrodes at aplurality of known, respective positions.

Preferably, the method comprises fixing the electrodes at the distal endof a catheter, and inserting the catheter into a chamber of the heart ofa subject, and wherein the velocity is a velocity of local electricalactivation in the endocardium. Preferably, the method bringing theelectrodes into contact with the endocardium, adjacent to the locationat which the velocity is to be determined. In a preferred embodiment ofthe invention, the velocity is a measure of ionic current.

In a preferred embodiment of the invention the method comprises bringingthe electrodes into proximity with a location in the brain, and whereinthe velocity is a velocity of local electrical activation in the brainof a subject.

In accordance with a preferred embodiment of the invention, there isfurther provided a method of mapping the velocity of local electricalactivation in a plurality of locations in the endocardium, comprisingdetermining the velocity at a plurality of known locations in thetissue, in accordance with the above described method, and recording thevelocity thus determined as a function of the respective knownlocations.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully understood from the followingdetailed description of the preferred embodiments thereof, takentogether with the drawings in which:

FIG. 1 is a generalized, conceptual schematic illustration of acatheter, in accordance with a preferred embodiment of the presentinvention;

FIG. 2 is a schematic illustration of a system incorporating thecatheter of FIG. 1, in accordance with a preferred embodiment of thepresent invention;

FIG. 3 is a schematic representation of a portion of the catheter ofFIG. 1, showing electrical signals as received at different sitesthereon, useful in understanding the operation of the invention;

FIG. 4A is a schematic, perspective representation of a system includinga catheter, to which electrodes are fixed, according to a preferredembodiment of the present invention;

FIGS. 4B-D are schematic drawings showings steps of calculating aconduction velocity in accordance with a preferred embodiment of theinvention;

FIG. 5 is a flow chart illustrating schematically a method ofdetermining the magnitude and direction of a vector, in accordance witha preferred embodiment of the present invention, as shown in FIGS. 4B-D;

FIG. 6A is a cross-sectional view of a catheter in a configurationsuitable for insertion into a patient's body and removal therefrom, inaccordance with one preferred embodiment of the invention;

FIG. 6B is a cross-sectional view of the catheter of FIG. 6A in analternative configuration suitable for performing electrophysiologicalmeasurements inside the body;

FIG. 7 is a three-dimensional graphic representation of the cathetershown in FIG. 6B;

FIG. 8A is a cross-sectional view of a catheter in a configurationsuitable for insertion into a patient's body and removal therefrom, inaccordance with another preferred embodiment of the invention;

FIG. 8B is a cross-sectional view of the catheter of FIG. 8A in analternative configuration suitable for performing electrophysiologicalmeasurements inside the body;

FIG. 8C is a perspective view of the catheter of FIG. 8A in a differentalternative configuration suitable for performing electrophysiologicalmeasurements inside the body;

FIG. 9 is a cross-sectional view of a catheter in accordance with analternative preferred embodiment of the invention, in a configurationsuitable for performing electrophysiological measurements inside thebody;

FIG. 10A is a perspective view of a catheter in accordance with stillanother preferred embodiment of the present invention, shown intransition from a closed configuration to an open configuration;

FIG. 10B is a perspective view of the catheter of FIG. 10A, shown in aclosed configuration suitable for insertion into and removal from ahuman body;

FIG. 10C is a perspective view of the catheter of FIG. 10A, shown in anopen configuration suitable for performing electrophysiologicalmeasurements inside the body;

FIG. 10D is a perspective view of the catheter of FIG. 10A having one ormore position sensors on the multiple arm structure;

FIG. 11A is a schematic, cross-sectional view of a catheter inaccordance with yet another preferred embodiment of the presentinvention, shown in a closed configuration suitable for insertion intoand removal from a human body;

FIG. 11B is a perspective view of the catheter of FIG. 11A, shown in anopen configuration suitable for performing electrophysiologicalmeasurements inside the body;

FIG. 12A is a schematic view of a catheter in accordance with stillanother preferred embodiment of the present invention, shown in acollapsed configuration suitable for insertion into and removal from ahuman body;

FIG. 12B is a schematic illustration of the catheter of FIG. 12A, shownin an expanded configuration suitable for performingelectrophysiological measurements inside the body;

FIG. 13A is a schematic view of a catheter in accordance with anotherpreferred embodiment of the present invention, shown in a collapsedconfiguration suitable for insertion into and removal from a human body;

FIG. 13B is a schematic illustration of the catheter of FIG. 13A, shownin an expanded configuration suitable for performingelectrophysiological measurements inside the body;

FIG. 14A is a simplified pictorial illustration of a catheter and acovering attached thereto, constructed and operative in accordance witha preferred embodiment of the present invention;

FIG. 14B is a front end view of the catheter of FIG. 14A

FIG. 14C is a front end view of a catheter distal end having a pluralityof arms wherein each arm has an electrode and a position sensor;

FIG. 15 is a simplified pictorial illustration depicting insertion ofthe catheter of FIG. 14A into a body vessel;

FIG. 16 is a simplified pictorial illustration of using the catheter ofFIG. 14A to sense a physiological activity of tissue inside a bodyorgan, in accordance with a preferred embodiment of the presentinvention;

FIG. 17 is a schematic illustration of a catheter with a control handle,in accordance with a preferred embodiment of the present invention; and

FIGS. 18A and 18B illustrate a steering mechanism in accordance with apreferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is now made to FIG. 1, which is a conceptual, schematicillustration of the distal end of a catheter 20 in accordance with apreferred embodiment of the present invention.

The catheter comprises an outer sheath or sleeve 22 and a substantiallyrigid ring 24 at the catheter's distal end. A plurality of sensorelectrodes 26, 28, 30 are fixed to ring 24 in such manner that when thering is placed against a biological tissue, such as the endocardium, theelectrodes receive electrical signals from the tissue. These signals areconveyed by conducting wires 31 inside sheath 22 to signal processingelectronics, not shown in the drawings.

Various modes of construction of electrodes 26, 28, 30, and signalprocessing electronics for electrophysiological measurements in theheart are known in the art and do not form, per se, a part of thepresent invention. The present invention may be used with any of thesemodes, as appropriate for the measurement being performed.

It will further be appreciated that while three electrodes are shown inthe schematic illustration of FIG. 1, in preferred embodiments of theinvention larger numbers of electrodes may be attached to ring 24, so asto enhance the accuracy of the electrophysiological measurements. Inother preferred embodiments of the present invention, ring 24 or anotherstructure at the distal end of catheter 20 may comprise only twoelectrodes. The two electrodes may be successively repositioned about alocation in the tissue so as to make multiple successive measurements,which are collectively used for determining the direction of a vector atthe location.

As will be explained in the discussion that follows, the threeelectrodes 26, 28 and 30, as shown in FIG. 1, are sufficient fordetermining the direction of a velocity vector in the biological tissuewith which they are in contact, in accordance with preferred embodimentsof the present invention. In other preferred embodiments of the presentinvention, however, larger numbers of electrodes may be attached to ring24. In such embodiments, the additional data provided by the greaternumber of electrodes may be used to determine the vector with greateraccuracy, or to resolve anomalous measurements due to pathologies in thetissue, for example.

Catheter 20 further comprises a device 32 for generating six-dimensionalposition and orientation coordinate information. Coordinate informationdevice 32 provides electrical signals via conducting wires 33 to signalprocessing electronics (not shown in the drawings), which determine thesix coordinates of translational position and angular orientation ofdevice 32 relative to an external frame of reference. In preferredembodiments of the present invention wherein catheter 20 is flexible,coordinate information device 32 is attached to ring 24 or is placedadjacent to the distal end of the catheter in a fixed, known relation toring 24, so that the position and orientation of ring 24 are knownrelative to device 32. In other preferred embodiments using rigidcatheters, for use in neurosurgery, for example, the coordinateinformation device may be located at any point along the length of thecatheter, although it is preferably located near the distal end.

In the context of this invention, the term substantially rigid, asapplied to ring 24 at the distal end of catheter 20, is taken to meanthat during successive measurements of electrophysiological signals bythe electrodes, the shape of the ring and its angular orientationrelative to coordinate information device 32 remain substantiallyunchanged. Consequently, the location of each of the electrodes on thering relative to coordinate information device 32 is substantiallyconstant, and thus the locations of all the electrodes relative to anexternal reference frame may be determined using the location andorientation information provided by the coordinate information device.During insertion and removal of the catheter from the body, however,this relationship may not be preserved.

In preferred embodiments of the present invention, catheter 20 is usedas part of a system for mapping physiological activity, as illustratedschematically in FIG. 2. A surgeon 21 inserts catheter 20 through anincision into a chamber of heart 23 of a patient 25, so that ring 24with its associated electrodes (not shown in FIG. 2) and coordinateinformation generating device 32 are inside the chamber. In accordancewith an exemplary position determination device described in PCT patentapplication number PCT/US95/01103, filed Jan. 24, 1995, and U.S. Pat.No. 5,391,199, which are assigned to the assignee of the presentapplication and whose disclosures are incorporated herein by reference,device 32 generates position signals in response to externally appliedmagnetic fields, generated by electromagnetic field generator coils 27,which are fixed to the operating table 29. Catheter 20 is connected atits proximal end via a cable 37, which contains conducting wires 31 and33 (shown in FIG. 1), to signal processing electronic circuits 39. Fieldgenerator coils 27 are similarly connected via cable 41 to drivercircuits 43. Circuits 39 and 43 are connected to a computer 51, whichcontrols their operation and receives signals therefrom, and which isalso coupled to monitor screen 53.

To map electrical activity in heart 23, surgeon 21 operates catheter 20so as to bring ring 24 to bear against a point on the endocardium 55.Circuits 39 receive and process position signals generated by device 32and electrical signals received by electrodes 26, 28 and 30 (shown inFIG. 1), and convey these signals to computer 51. The computer uses theprocessed signals to determine the locations of electrodes 26, 28 and 30and to compute a local electrical activation vector 38, as will bedescribed below with reference to FIG. 3. The surgeon operates thecatheter so as to move the ring to multiple other points on theendocardium, repeating the above steps at each such point. The computeruses the signals receive at the multiple points to generate a map ofvector 38, which is displayed, along with other useful data, on monitorscreen 53. The map may also be stored and recorded for later use, bymeans and methods known in the art.

Preferably, measurements by coordinate information device 32 aresubstantially synchronized with the heart cycle, with all measurementsmade during diastole, for example, so as to eliminate errors, that mayarise in determining positions of electrodes 26, 28 and 30, due tomovement of the heart. The electrodes, however, remain fixed in theirpositions adjacent to the endocardium during all parts of the heartcycle, until the surgeon moves them.

The operation of the present invention will be better understood byreference to FIG. 3, which shows ring 24 and electrodes 26, 28, 30thereon, together with representations of electrograph signals 34, 35,36 that are typically received from electrodes 26, 28, 30, respectively,when the ring is positioned so that the electrodes are in contact withthe endocardium. Signals 34, 35 and 36 are shown schematically forexplanatory purposes only. For the signals shown, vector {right arrowover (V)} 38 represents the direction of an electrical activation vectorin the endocardium at the location of the ring.

As indicated by the direction of vector {right arrow over (V)}, thesharp electrical impulse peak shown in graphs 34, 35 and 36 will reachelectrode 26 first, at time t₁, and subsequently electrode 28, at timet₂, and finally, electrode 30, at time t₃. Typically such a sharpelectrographic impulse peak, which is seen in the well-known QRS portionof the electrocardiogram waveform, propagates through the heart muscleto induce contraction.

The relative time of arrival of the signal peak at each of theelectrodes can thus be used to determine the magnitude and direction of{right arrow over (V)} relative to ring 24. Referring to FIG. 3, we noteby way of example that the time difference between the signal peaks atelectrodes 26 and 28, τ₂=t₂−t₁, is roughly twice the time difference forelectrodes 26 and 30, τ₃=t₃−t₁. This temporal measurement indicates thatthe electrical activation wave front passing electrode 26 takes twice aslong to reach electrode 30 as it does to reach electrode 28, and thusthat vector {right arrow over (V)} points from the position of electrode26 toward that of electrode 30. If the ratio τ₂/τ₃ were relativelysmaller, {right arrow over (V)} would be found to be rotated clockwiserelative to the direction shown in FIG. 3, while if the ratio werelarger, {right arrow over (V)} would be rotated counterclockwise.

Although the above example and preferred embodiments of the presentinvention described herein refer specifically to three electrodes andsignals received therefrom, it will be understood that preferredembodiments of the present invention may comprise four or moreelectrodes. The additional arrival time data provided by the largernumber of electrodes may be used to determine the direction of {rightarrow over (V)} with greater accuracy.

Other preferred embodiments of the present invention may include onlytwo electrodes, in which case a single measurement will give a generalindication of the direction of {right arrow over (V)}, and multiple,sequential measurements may be used to determine the direction of {rightarrow over (V)} with greater accuracy. It is generally preferable,however, that the distal end of the catheter comprise at least threenon-collinear electrodes, so that the vector {right arrow over (V)} maybe fully determined as shown in FIG. 3.

Although in FIG. 3 the amplitudes of signals 34, 35 and 36 are allroughly the same, at certain locations in the endocardium, andparticularly in the vicinity of pathological areas of the heart, therelative amplitudes of the signals may vary, and these amplitudevariations may also be useful in locating and diagnosing the pathology.

For example, pairs of electrodes, such as electrodes 26 and 28, may becoupled together so as to act as bipolar electrodes. In this case, thesignal processing electronics will detect the electrical potentialdifference between electrodes 26 and 28, for example, correspondingsubstantially to the local electrical activity between the electrodes.If, in this example, the direction of the local electrical activationvector {right arrow over (V)} has a large component directed fromelectrode 26 toward electrode 28, the bipolar signal measured betweenthese electrodes will have relatively large amplitude. If the vector hasa large component directed from electrode 28 toward electrode 26, thebipolar signal will also have relatively large amplitude, although ofopposite sign to that of the preceding case. If, however, the vectorpoints in a direction substantially perpendicular to an axis passingthrough electrodes 26 and 28, the amplitude of the bipolar signal willbe relatively small or zero.

It will be understood that any direction of the vector {right arrow over(V)} can be decomposed into components parallel and perpendicular to anaxis passing through a pair of electrodes, and the amplitude of thebipolar signal between these electrodes will be proportional to therelative magnitude of the parallel component. Thus, by integrating thearea under the bipolar signal peak with respect to time, and comparingthe integrated signals obtained from two or more electrode pairs, thedirection of the local electrical activation vector {right arrow over(V)} can be determined using the relative amplitudes rather than thearrival times of the signal peaks.

Since the position and orientation of ring 24, relative to the distalend of catheter 20 and coordinate information device 32, are known, thedirection of vector {right arrow over (V)} can be determined relative tothe external frame of reference. This external fame of reference ispreferably substantially fixed in relation to the heart muscle, usingmethods that will be discussed in greater detail below. By moving thedistal end of the catheter from location to location inside the heartand repeating the measurement of signals 34, 35, 36, a map of {rightarrow over (V)} as a function of position on the surface of theendocardium may be conveniently generated.

Another method of conduction velocity determination, in accordance witha preferred embodiment of the invention, calculates the velocity vectoras being perpendicular to local isochronals of an activation front(marked as IS in FIG. 4C). FIG. 4A shows a structure 240 at the distalend of a catheter 220, which is similar to the structure of FIGS.10A-10C. Structure 240 at the distal end of catheter 20, comprises aplurality of arms 242 to which electrodes 226, 228 and 230 are fixed inknown relative positions. Preferably the electrodes are placed intocontact with the endocardium of the heart of a subject, and generatelocal electrogram signals in response to electrical potentials in theendocardium. These signals are preferably conveyed through arms 242 andcatheter 220 to signal processing apparatus 248, which processes thesignals to determine a local activation time at the respective positionof each of the electrodes.

It will be understood that while catheter 220 is useful in conjunctionwith preferred embodiments of the present invention, it is shown in FIG.4A only by way of illustration, for clarity in describing a method ofvelocity determination, in accordance with preferred embodiments of thepresent invention. The method of the present invention as describedbelow may similarly be used in conjunction with other types ofstructures that allow for placement of electrodes at known, spacedpositions in contact with physiological tissue, such as those describedherein.

A Cartesian coordinate frame 244 is defined by the positions of thecatheter and the electrodes, wherein the Z-axis is aligned with the longaxis of catheter 220, the Y-axis is defined by a line normal to theZ-axis and passing through electrode 226, and the X-axis isperpendicular to both the Y- and the Z-axes. The positions of electrodes226, 228 and 230 are marked respectively as A, B and C in the figure incoordinate system 244, for clarity in the explanation that follows.

As shown in FIG. 4A, position- and orientation-responsive signalsgenerated by device 232 are conveyed to position sensing apparatus 246,which uses the signals to compute position and orientation coordinatesof the catheter relative to a reference frame 250, comprising K, L and Maxes as shown in FIG. 4A, defined by external radiator coils 27, whichgenerate the magnetic fields.

Preferably, the position of the origin and the orientation of frame 244are calibrated in relation to frame 250, before beginning to measure andmap the electrical activation time. To perform this calibration, thedistal portion of catheter 220 is placed in a known location andoriented so that each of the X, Y and Z axes of coordinate frame 244 issubstantially aligned with one of the K, L and M axis of coordinateframe 250. The position and orientation coordinates of catheter 220 atthis location and orientation, as computed by position sensing apparatus246, are then recorded and used subsequently as zero-reference points incomputing position and orientation coordinates of the catheter duringmeasurement and mapping. Preferably, at least one of the electrodes isselected as the reference electrode and is aligned with one of axes K, Lor M. Alternatively, to using frame 250, a local reference frame, suchas one coupled to the heart may be used, as described herein.

FIGS. 4B-D and 5 illustrate a method, in accordance with preferredembodiments of the present invention, for mapping a vector velocity ofelectrical activation {right arrow over (V)}, as a function of lime, inthe endocardium, using catheter 20 or similar apparatus. FIG. 5 is aflowchart of the method, while FIGS. 4B-D illustrate the method on aschematic of electrodes 226, 228 and 230. First, the catheter is broughtinto contact with a location in the endocardium, and positions A, B andC are determined, corresponding to the respective positions ofelectrodes 226, 228 and 230 and to respective portions of theendocardium. It will be appreciated that, in accordance with preferredembodiments of the present invention described herein, it is sufficientto determine the position and orientation of distal end of catheter 20,in order to determine A, B and C.

Next, local electrical activation times, τ_(A), τ_(B) and τ_(C),respectively, arc measured by signal processing apparatus 48 at therespective positions of the electrodes. Measurement of electricalactivation time is performed according to methods known in the art, forexample by sensing sharp peaks in the electrogram signals received fromthe electrodes and determining thereby the relative time at which thelocal tissue depolarizes, as described above in reference to FIG. 3.

The depolarization time can be determined using bipolar electrodes, forexample, by coupling together pairs of electrodes, such as electrodes226 and 228, so as to act as bipolar electrodes. In this case, thesignal processing electronics will detect the electrical potentialdifference between electrodes 226 and 228, for example, correspondingsubstantially to the local electrical activity between the electrodes.If, in this example, the direction of the local velocity vector {rightarrow over (V)} has a large component directed from electrode 26 towardelectrode 28, the bipolar signal measured between these electrodes willhave relatively large amplitude.

In a preferred embodiment of the invention, each of electrodes 226, 228and 230 is a bipolar electrode comprised of two individual electrodes).

The local electrical activation times are compared so as to identify oneof electrodes 226, 228 and 230 whose local electrical activation time isnot equal to those of the other two electrodes. If such an electrodecannot be found, i.e., the local activation times of all threeelectrodes are equal or cannot be measured, then the local activationvelocity {right arrow over (V)} is determined to be zero, and thelocation in the endocardium with which the catheter is in contact isidentified as a suspected site of pathology, for example a source orsink of electrical activation. In a preferred embodiment of theinvention, catheter 220 is preferably moved to a new location on theendocardium, which location is a short distance from the previouslocation, such that there is substantial overlap in the endocardiumwhich is mapped in the new location and in the previous location. Thus,it is possible to identify whether the previous location is a source, asink, or possibly, dead scar tissue. It should be appreciated, that suchprecise relocalization is made possible using position sensing device232.

In another preferred embodiment of the invention, a velocity map isrepeated after a medical procedure, such as surgery or an ablation (evenof a single point) and/or after a different pacing scheme is sued. Thus,the effect of such procedures on the conduction velocity is easilydetermined. Such temporally repeated mappings can be used to asses theadvance of arrhythmias, as one effect of abnormal conduction is that theconduction velocity changes with time. In addition, the vector of thedepolarization potential changes during the cardiac cycle. Measuringthis vector, even at a single location in the heart, can provide muchinformation regarding the functioning of the heart. If four non-coplanarelectrodes are provided for in the catheter, the three-dimensionalpotential vector of the heart may be determined.

In the following discussion (FIGS. 4C and 4D), the electrode found tohave the latest activation time, τ_(max), is marked “c”, the electrodewith the earliest activation time, τ_(min), is marked “d”, and theelectrode with the intermediate activation time, τ_(between), is marked“b”.

A point “a” indicates a (calculated) location on the line connecting “c”and “d” which has the same activation lime as electrode “b”. The localisochronals are all assumed to be parallel to line “ab”, which connectspoint “a” and point “b”. Clearly, as the distance between electrodes226, 228 and 230 decreases, the validity of this assumption increases,as does the precision of the method.

If two electrodes are found to have the same activation time (within anε), the local isochronals are assumed to be all parallel to the lineconnecting the two electrodes, and the velocity vector is perpendicularto the connecting line.

{right arrow over (V)} is now computed, based on the followingprocedure, illustrated by FIG. 4C. Point “p” is located on the line “ab”connecting points “a” and “b”, such that velocity vector {right arrowover (V)} is perpendicular thereto. Using vector arithmetic:

{right arrow over (A)}b=a−b  (1)

{right arrow over (C)}b=c−b  (2)

$\begin{matrix}{{\cos \quad \alpha} = \frac{\overset{\rightarrow}{A}{b \cdot \overset{\rightarrow}{C}}b}{{{\overset{\rightarrow}{A}b}} \cdot {{\overset{\rightarrow}{C}b}}}} & (3) \\{{p - b} = {{{{\overset{\rightarrow}{C}b}} \cdot \cos}\quad \alpha \quad \frac{\overset{\rightarrow}{A}b}{{\overset{\rightarrow}{A}b}}}} & (4) \\{p = {b + {{{{\overset{\rightarrow}{C}b}} \cdot \cos}\quad \alpha \quad \frac{\overset{\rightarrow}{A}b}{{\overset{\rightarrow}{A}b}}}}} & (5)\end{matrix}$

 {right arrow over (C)}p=c−p  (6)

$\begin{matrix}{\overset{\rightarrow}{V} = \frac{\overset{\rightarrow}{C}p}{\tau_{\max} - \tau_{\min}}} & (7)\end{matrix}$

In a vector based approach, A, B and C are vector coordinates of theelectrodes (in reference frame 244 or 250 ) and are referred to as{right arrow over (A)}, {right arrow over (B)} and {right arrow over(C)}.

A method, in accordance with preferred embodiments of the presentinvention, for mapping a vector velocity of electrical activation {rightarrow over (V)}, as a function of time, in the endocardium, usescatheter 20 or similar apparatus; First, the catheter is brought intocontact with a location in the endocardium, and vectors {right arrowover (A)}, {right arrow over (B)} and {right arrow over (C)}, aredetermined, corresponding to the respective positions of electrodes 226,228 and 230. It will be appreciated that in accordance with thepreferred embodiment of the present invention described with referenceto FIG. 4A, it is sufficient to determine the position and orientationof distal end of catheter 220, in order to determine {right arrow over(A)}, {right arrow over (B)} and {right arrow over (C)}.

Next, local electrical activation times, τ_(A), τ_(B) and τ_(A),respectively, are measured by signal processing apparatus 48 at therespective positions of the electrodes. Measurement of electricalactivation time is performed according to methods known in the art, forexample by sensing sharp peaks in the electrogram signals received fromthe electrodes and determining thereby the relative time at which thelocal tissue depolarizes, as described above in reference to FIG. 3.

Next, the local electrical activation times are compared so as toidentify one of electrodes 226, 228 and 230 whose local electricalactivation time is not equal to those of the other two electrodes. Ifsuch an electrode cannot be found, i.e., the local activation times ofall three electrodes are equal or cannot be measured, then the localactivation velocity {right arrow over (V)} is determined to be zero, andthe location in the endocardium with which the catheter is in contact isidentified as a suspected site of pathology, for example a source orsink of electrical activation.

In the following discussion, we will assume that electrode 226 is foundto have a local electrical activation time different from those ofelectrodes 228 and 230, and is thus taken as a reference point fordetermination of {right arrow over (V)}. It will be appreciated,however, that the method described below will be equally applicable ifeither electrode 228 or electrode 230 is thus found and taken as thereference.

{right arrow over (V)} is now computed, based on the followingprocedure. Velocity component vectors {right arrow over (P)}_(B) and{right arrow over (P)}_(C) are determined based on the measuredelectrode positions and local electrical activation times:$\begin{matrix}{{\overset{\rightarrow}{P}}_{B} = \frac{\overset{\rightarrow}{B} - \overset{\rightarrow}{A}}{\tau_{B} - \tau_{A}}} & (8) \\{{\overset{\rightarrow}{P}}_{C} = \frac{\overset{\rightarrow}{C} - \overset{\rightarrow}{A}}{\tau_{C} - \tau_{A}}} & (9)\end{matrix}$

{right arrow over (P)} _(CB) ={right arrow over (P)} _(B) −

{right arrow over (P)}_(C)  (10)

$\begin{matrix}{{\hat{P}}_{CB} = \frac{{\overset{\rightarrow}{P}}_{CB}}{{\overset{\_}{P}}_{CB}}} & (11) \\{\overset{\rightarrow}{V} = {{\overset{\_}{P}}_{B} - {\left( {{\hat{P}}_{CB} \cdot {\overset{\_}{P}}_{B}} \right){\hat{P}}_{CB}}}} & (12)\end{matrix}$

It will be appreciated from equation (10) that if τ_(B)=τ_(C), then{right arrow over (P)}_(CB) will be normal to an axis passing throughpoints B and C, which correspond to the positions of electrodes 224 and226 respectively.

One advantage of using this second, vector based, method is itssimplicity. Another advantage is that the electrode plane need not beperpendicular to the catheter. A further advantage is that the velocityis unambiguously determined. It should be noted that the determinedvelocity vector is in the coordinates of the heart, not of the catheter,since the transformation between the internal and external framescancels out when the calculations of equations (8)-(12).

Catheter 20 is then moved to another location, and the proceduredescribed above is repeated multiple times, so as to generate a map of{right arrow over (V)} as a function of location in the endocardium.Preferably this map is used to determine locations of defects in thepropagation of electrical activation in the endocardium, particularly tofind sources and sinks of the activation. The map may further becompared with maps generated at earlier times, so as to identify changesin the local activation velocity over time.

In preferred embodiments of the present invention, ring 24 is made ofresilient material. During insertion of the catheter through thepatient's blood vessels and into the heart chamber, the ring iscollapsed into an elongated shape so as to pass easily through the bloodvessels. In the preferred embodiment shown schematically in FIG. 6A,during such insertion, the ring is contained inside catheter sheath 22.The ring is coupled to a stiff pushing member 40, which extends theentire length of the catheter. Position information device 32 is alsocoupled to pushing member 40, proximal to ring 24.

As shown in FIG. 6B, once the distal end of the catheter has beenpositioned inside the heart chamber, pressure is exerted on pushingmember 40, and ring 24 is ejected through slot 42 in the surface 43 ofthe distal end of the catheter. The resilience of the ring then causesit to assume its desired, preferably circular, shape, which is broughtinto contact with surface 43. Position information device 32simultaneously assumes its desired position adjacent to the distal endof catheter 20 inside sheath 22. Alternatively, coordinate informationdevice 32 may be fixed in a constant position inside sheath 22,unaffected by the movement of pushing member 40.

Preferably ring 24 is formed from a resilient, super-elastic material,such as NiTi. Such materials have the property that when a piece of thematerial is heated above a certain critical temperature, it may be bentor formed into a desired shape. If the material held in this shape whileit is cooled to below the critical temperature, then it willsubsequently resiliently retain the given shape. Thus, although it maybe compressed or bent by exertion of sufficient force, once the force isremoved, the super-elastic material will return resiliently to its givenshape, in this case a ring.

When the catheter is to be withdrawn from the heart, pushing member 40is pulled back, thereby drawing ring 24 back through slot 42, reassumingthe shape shown in FIG. 6A.

As shown in FIG. 7, which is a perspective view of the preferredembodiment of FIGS. 6A and 6B, in a preferred embodiment of the presentinvention, ring 24 is formed from a flat strip of material, which isbent into a ring shape. Once the ring has been ejected from thecatheter, its elasticity causes it to bear against the edges of slot 42,so as to hold the ring in a known angular orientation relative to theaxis 45 of the catheter and prevent rotation in a direction, indicatedby ψ, about axis 45, as shown in FIG. 7. The flat shape of the ringmaterial effectively prevents the ring from tilting in an up-downdirection, indicated by θ, relative to axis 45. The flat surface of thering also bears against the flat surface 43 of the distal end of thecatheter, thereby preventing wobble of the ring in a side-to-sidedirection, indicated by φ, relative to axis 45. Thus, since thegeometrical shape and dimensions of ring 24 are known, and its angularorientation relative to catheter axis 45 is substantially fixed, thelocations of electrodes on the ring can be determined from thesix-dimensional position and orientation data provided by coordinateinformation device 32.

Preferably, electrodes 26, 28 and 30 extend to and, more preferably,extend below or around the lower edge of ring 24.

In another preferred embodiment of the present invention, shown in FIGS.8A and 8B, electrodes 26, 28, 30 are attached to a ring 44 formed from ahollow section of substantially rigid material, such as a tube, which isclosed off at its distal end. The ring is rigidly coupled to the distalend of catheter 20, so that its geometric shape and angular orientationrelative to the axis of the catheter are known. Ring 44 also comprisescoordinate information device 32 adjacent to its distal end.Alternatively, device 32 may be located in catheter 20.

When the catheter is to be inserted through the patient's blood vesselsand into the heart, a stylette 46 is inserted from the proximal end ofthe catheter, through catheter sheath 22 and into the lumen of the tubefrom which ring 44 is formed, thereby straightening the ring as shown inFIG. 8A. Only the distal end of stylene 46 is substantially rigid, andthe remaining length of the wire may be flexible, as long as it is stiffenough to allow it to be pushed into the hollow center of ring 44 forinsertion and removal of the catheter from the heart.

Once the distal end of the catheter is inside the heart chamber,stylette 46 is withdrawn, and ring 44 resumes its predetermined circularshape and orientation, as shown in FIG. 8B.

In another preferred embodiment of the present invention, shown in FIG.8C, ring 44 is so formed that when stylette 46 is withdrawn, the ringtwists sideways, so that the axis of the ring is substantially parallelto the long axis of catheter 20. In this twisted orientation of ring 44,electrodes 26 (not shown), 28 and 30 attached to the ring may moreeasily be brought into contact with the endocardium.

In yet another, similar preferred embodiment of the present invention,ring 44 at the distal end of the catheter is formed of a hollow sectionof flexible material. For insertion or removal of the catheter from thebody, this hollow section is straightened by insertion of a straightstylette 46 into the lumen of the hollow section. After insertion of thecatheter into the heart, the straight stylette is withdrawn, and asecond stylette (not shown in the figures), formed of substantiallyrigid material and including a curved portion at its distal end, isinserted. For insertion of this second stylette through a lumen of thecatheter, the curved distal portion of the stylette is straightened, andthe relative stiffness of the catheter causes the stylette to remainstraight as it is passed through the catheter. When this stylettereaches the hollow, flexible section 44 at the distal end of thecatheter, however, the resilience of the stylette causes its distalportion to resume its curved shape, and thus causes the hollow, flexiblesection of the catheter to curve, as well, into the desired ring shape.

In some preferred embodiments of the present invention in which thedistal end of the catheter is straightened during insertion into theheart, when the section at the distal end of catheter 20 is caused tocurve into a ring 44 after insertion, as shown in FIG. 7, distal tip 47of the ring section engages a socket 49 in the side of the catheter.Fluoroscopy or other methods of imaging known in the art may be used toobserve ring 44 at the distal end of the catheter and verify that distaltip 47 of the distal section has engaged socket 49, so as to ensure thatthe ring has assumed its desired shape and orientation prior tobeginning electrophysiological measurements.

Alternatively, in some preferred embodiments of this type, distal tip 47of the distal section of the catheter comprises a first electricalcontact, not shown in the figures, and socket 49 in the side of thecatheter comprises a second electrical contact, likewise not shown. Whendistal tip 47 engages socket 49, the first electrical contact is broughtinto proximity with the second electrical contact. The mutual proximityof the contacts is measured electrically using methods known in the art,so as to verify that the distal tip has engaged the socket.

Although the above preferred embodiments are described with reference torings having flat or round cross-sectional profiles, it will beappreciated that other preferred embodiments of the present inventionmay comprise structures having other geometrical shapes and/or othercross-sectional profiles for placement of electrodes. Thecross-sectional profile of the structure may be non-uniform.Furthermore, although the electrodes are shown in the figures as beingattached externally to rings having smooth outer surfaces, in otherpreferred embodiments of the present invention, the rings may includerecesses into which electrodes or other sensors are inserted.

In one such preferred embodiment of the present invention, theelectrodes are placed on a structure comprising rigid and flexible,resilient sections. For insertion and removal of the catheter, theflexible sections bend, causing the structure on which the electrodesare placed to collapse into a narrow shape. The resilience of thesesections, however, causes the structure to open out for makingmeasurements once inside the heart.

Any desired geometrical structure may be used for electrode placement inaccordance with the present invention, as long as the catheter and oneor more devices for generating coordinate information are configured toallow determination of locations of all the electrodes. For example, ina preferred embodiment of the present invention comprising multipledevices for generating three-dimensional location information, one suchdevice is placed adjacent to each of the electrodes, so that it is notnecessary to explicitly determine the angular orientation of thestructure holding the electrodes.

In some preferred embodiments of the present invention, the structure inwhich the electrodes are placed at the distal end of the catheter ispolygonal, most preferably triangular. When the vertices of thepolygonal structure are brought into contact with the endocardium, theywill typically lodge in small crevices in the heart tissue, thuspreventing the structure from moving during measurement, despite thenatural motion of the heart. Preferably the electrodes are attached ator near the vertices.

In another preferred embodiment of the present invention, shown in FIGS.10A, 10B and 10C, structure 60 at the distal end of the cathetercomprises multiple arms 62, 64 and 66. Electrodes 26, 28 and 30 areattached to the respective arms. As shown most clearly in FIG. 10A, arm62 comprises two substantially rigid sections 68 and 70, which arejoined by resilient joint 72. This joint is formed in such a manner thatit causes sections 68 and 70 to maintain a mutual alignment that issubstantially collinear, as shown in FIG. 10B, when no external forcesare exerted thereon. (Although for the sake of simplicity, sections 68and 70 and joint 72 are marked in FIG. 10A only with respect to arm 62,it will be understood that arms 64 and 66 are similarly constructed.)The arms are joined at their proximal ends to the distal end of catheter20. The distal ends of the arms are joined together at flexible joint74. Draw-wire 76 is also connected at its distal end to joint 74, andpasses through a lumen of catheter 20 to its proximal end (not shown).

As shown in FIG. 10B, during insertion of catheter 20 into the heart orremoval therefrom, draw-wire 76 is released, and the resilience ofjoints 72 causes sections 68 and 70 to maintain a substantiallycollinear mutual alignment, parallel to the long central axis 45 of thecatheter. Once the catheter has been inserted into the heart, draw-wire76 is pulled back toward the proximal end of catheter 20, exerting aproximally-directed force on flexible joint 74, and thereby causingresilient joints 72 to flex, as shown in FIG. 10A.

As shown in FIG. 10C, when draw-wire 76 is pulled completely into thecatheter, joint 72 flexes by approximately 180° relative to its initialposition (i.e., the position shown in FIG. 10B). Sections 68 and 70assume mutually adjacent positions, in substantially parallel mutualalignment, extending radially outward from and approximatelyperpendicular to catheter axis 45. In this configuration, electrodes 26,28 and 30 may be brought into contact with the endocardium formeasurement of electrical potentials. One or more devices for generatingcoordinate information 32 (shown in FIG. 10D) may be fixed to structure60 or adjacent to the distal end of catheter 20.

In another preferred embodiment of the present invention, shown in FIGS.11A and 11B, electrodes 26, 28 and 30 arc fixed adjacent to and alignedwith the distal ends of substantially rigid arms 80, 82 and 84respectively. As shown in FIG. 11A, during insertion of catheter 20 intothe heart or removal therefrom, the arms are contained inside respectivelumens 85, 86 and 87 of the catheter, wherein the distal ends of thearms are adjacent to small radial openings 88, 90 and 92, respectively,in sheath 22 of the catheter. A device 32 for generating coordinateinformation is adjacent to the distal end of the catheter.

Once catheter 20 has been inserted into the heart, arms 80, 82 and 84are pushed out through their respective radial openings, as shown inFIG. 11B. The resilience of the arms causes electrodes 26, 28 and 30 toassume predetermined positions, distal to the catheter's distal end andmutually-spaced about its long central axis 45.

Despite the flexibility of catheters, it is sometimes difficult to pushthe catheter smoothly through convolutions of certain vessels. Inparticular, the distal end of the catheter may chafe or scrape an innersurface of the vessel, not only making the insertion of the catheterdifficult, but possibly causing damage to the vessel. Anotherpossibility of damage occurs after the distal end of the catheter hasentered an organ such as a chamber of a heart. Since the distal end isusually thin, care must be exercised to prevent accidentally puncturing,scraping or otherwise damaging inner walls of the organ.

Another problem relates to the possibility of formation of blood clotsin cracks or sharp comers which are formed at the tip of the catheter.

One solution to these problems is to provide the catheter with a soft,smooth tip. In a preferred embodiments of the invention, the structureto which electrodes are fixed at the distal end of the catheter iscoupled to an inflatable element, such as a balloon. After the catheterhas been inserted into the heart, the inflatable element is inflated andcauses the structure to assume a predetermined, known shape andorientation relative to the distal end of the catheter.

Thus, in a preferred embodiment of the present invention shown in FIGS.12A and 12B, a catheter 20 comprises a balloon 93 at the catheter'sdistal end, wherein electrodes 26, 28 and 30 are attached to the surfaceof the balloon. The electrodes may be mechanically fastened to theballoon, or they may be chemically deposited on the balloon's surfaceusing methods of electroplating or coating known in the art. Balloon 93contains and protects a wire basket structure 94, which typicallyincludes lateral wires 95 and axial wires 96 connected to electrodes 26,28 and 30. Wires 95 and 96 are flexible, so that they may bend freely,but they are non-extensible, i.e., their length remains substantiallyconstant when a tensile, stretching force is applied to them. Axialwires 96 are connected at their proximal ends to an anchor 97, which isin turn connected to a device 32 for generating coordinate information.

As shown in FIG. 12A, during insertion of catheter 20 into the heart,balloon 93 is deflated, thereby causing wires 95 and 96 to bend, so thatbasket structure 94 collapses into a narrow elongated shape.

Then, once the catheter is inside a chamber of the heart, as shown inFIG. 12B, balloon 93 is inflated by methods known in the art, such as byintroducing a fluid into the interior thereof through a lumen of thecatheter (not shown in the figure). Inflation of balloon 93 causesbasket structure 94 to expand and become substantially rigid. When theballoon is fully inflated, wires 95 and 96 are pulled taut, so thatelectrodes 26, 28 and 30 assume known positions, relative to one anotherand relative to anchor 97, as determined by the lengths of wires 95 and96. Because the wires are non-extensible, additional inflation ofballoon 93 beyond the size necessary to straighten the wires will notaffect the relative positions of the electrodes. For removal of thecatheter from the body, balloon 93 is again deflated.

In another preferred embodiment of the present invention, shown in FIGS.13A and 13B, catheter 20 comprises at its distal end a balloon 93 and acollapsible structure 98. Structure 98 includes a substantially rigidaxial member 99, which is contained inside balloon 93, and a pluralityof radial members 101 coupled to the balloon on its outer surface.Radial members 101 comprise joints 103, so that when the balloon isdeflated, as shown in FIG. 13A, the radial members fold down, andstructure 98 assumes an elongated, narrow shape for ease of insertioninto the body. Electrodes 26, 28 and 30 are fixed to the distal ends ofradial members 101. Axial member 99 is attached at its proximal end toanchor 97, which is in turn connected to a device 32 for generatingcoordinate information. Structure 98 further comprises flexible,non-extensible wires 105, each of which is respectively attached at itsproximal end to a point on axial member 99 or anchor 97, and at itsdistal end to a point adjacent to the distal end of a respective radialmember 101.

As shown in FIG. 13B, after catheter 20 has been inserted into theheart, balloon 93 is inflated, thereby causing joints 103 to straighten,so that radial members extend radially outward from a central axisdefined by axial member 99. When the balloon is fully inflated, wires105 are pulled taut, thereby constraining joints 103 from bending anyfurther than desired. Structure 98 thus becomes substantially rigid, sothat electrodes 26, 28 and 30 assume known positions, relative to oneanother and relative to anchor 97, as determined by the structure.Because the wires are non-extensible, additional inflation of balloon 93beyond the size necessary to straighten the wires will not affect therelative positions of the electrodes.

It should be appreciated that the electrodes deposited on the balloonmay be of any desirable configuration, including, three unipolarelectrodes, three bipolar electrodes, a line of electrodes. In addition,the balloon/structure may be adapted for a particular body structure,such as near the mitral valve, by suitable design of the inflated formof the balloon/structure.

Reference is now made to FIG. 14A which illustrates a catheter 310 and acovering 312 attached thereto, constructed and operative in accordancewith a preferred embodiment of the present invention.

Catheter 310 may any known type of catheter suitable for insertion intoa body vessel, and preferably includes a tubular body portion 314 havinga distal end 316.

Covering 312 preferably includes a resilient cap member 320 extendingdistally from distal end 316. Resilient cap member 320 preferablyincludes a tuft of distally extending, resilient lobes 322 with soft,smooth outer surfaces. Resilient cap member 320 is preferablyconstructed of an elastomeric material, such as rubber or latex. Lobes322 are preferably substantially symmetrically arranged about alongitudinal axis 324 of catheter 310. FIG. 14A illustrates three lobes322 substantially mutually spaced 120° apart about axis 324. It isappreciated that covering 312 may alternatively comprise any othernumber of lobes 322, including only a single off-axis lobe.

Preferably a sleeve 326 extends from a proximal end 328 of resilient capmember 320 and snugly fits over distal end 316 of the catheter. At leastone radial dimple 330 is preferably formed at a juncture between sleeve326 and the resilient cap member 320. In accordance with one aspect ofthe present invention, the radial dimple makes it easier for the lobesto bend backwards, by providing a volume to accommodate a portion of thelobe and enable a sharper bend angle with less stress on the cap. Inaccordance with a second aspect of the present invention, the dimplestrengthens the connection between covering 312 and catheter 310.

Preferably at least one sensor 332 is fixed to resilient cap member 320.As seen in FIG. 14A, most preferably one or more sensors 332 areembedded inside each lobe 322. Sensors 332 may be any type of sensoruseful in sensing a physiological activity. Sensor 332 may include amonopolar electrode or a bipolar electrode, useful for determining localelectrical activity, such as local activation time. Alternatively oradditionally, sensor 332 may include a strain gauge useful fordetermining muscle contraction. Sensors 332 may be in wiredcommunication with sensor processing equipment (not shown) by means ofwires 334 which are preferably embedded in lobes 322 along with sensors332. Alternatively, sensors 332 may be capable of wireless transmissionto sensor processing equipment (not shown).

In a preferred embodiment of the invention, (as shown in FIG. 14C), aposition sensor 32 having one or more coils 32 a is embedded in lobe322, preferably near sensor 332, so as to more exactly determine therelative position of sensor 332.

One aspect of electrophysiological mapping is assuring that sensors 332do not slip along the myocardium during the cardiac cycle. As shown inFIG. 14A, there may be provided at least one bump 336 which protrudesfrom lobe 322 of resilient cap member 20. All or a portion of lobes 322may be provided with one or more bumps 336. Bump 336 is preferablyintegrally formed with lobe 322. In accordance with a preferredembodiment of the present invention, the bump 336 may include thereinone or more of the sensors 332. It is appreciated that lobe 322 may haveone sensor 332 inside bump 336 and another sensor 332 outside of bump336. Bumps 336 may also serve to enhance the tissue contact and sensingcapability of sensors 332. In particular it is understood that for bestresults in most sensing regimes a path from the sensor should beprovided to the contact point on the surface of the myocardium. Thenature of this path which may be a conducting path to the end of a bump,depends on the nature of the measurement being performed.

FIG. 14B shows a front view of catheter 310. The lack of any sharpangles in this embodiment should be appreciated. In a preferredembodiment of the invention, at least one opening 333 to a lumen isformed in each lobe 322. Such a lumen may be used to provide anextendible barb for attaching the lobe to the myocardium. Alternatively,such a lumen may be connected to a vacuum pump to provide anchoring viasuction. Further alternatively, such a lumen may be used to provideirrigation to the region of sensor 332. Preferably, anchoring means suchas barbs and suction are applied only after sensor 332 is in goodcontact with the myocardium. The quality of contact is preferablydetermined using electrical activity signals and/or impedance signalsfrom sensors 332.

In another preferred embodiment of the invention cap 320 includes asensor 335 which generates indications of the relative positions oflobes 322. Sensor 335 may be a strain gauge which generates AC signalswhen lobes 322 move in relation to each other and/or in relation tocatheter 310. Alternatively, sensor 335 may be a fiber-optic bendsensor. In one preferred embodiment of the invention, each of lobes 322has an embedded sensor 335. Alternatively, all of lobes 322 areconnected to a single sensor. In one preferred embodiment of theinvention, local contraction time is determined based on the signalgenerated by sensor 335. It should be appreciated that binaryinformation (constant strain/change in strain) is enough to determinethe onset of such movement. However, preferably, the resolution of thesignal from sensor 335 is sufficient to determine the relative positionsof lobe 322 and cap 320.

In a preferred embodiment of the invention, local electromechanicalmapping is performed even without a position sensor. One type of suchmapping is viability mapping in which the relative timing of theelectrical activation and the muscle contraction are compared. Further,such a strain gauge can be used in any of the multi electrodeembodiments described herein.

Reference is now made to FIG. 15 which illustrates inserting catheter310 into a body vessel 340 in a distal direction, indicated by an arrow342. Resilient cap member 320 and/or its lobes 322 are resilientlyinverted over distal end 316 of catheter 310 during the distallydirected motion of catheter 310 in vessel 340. Lobes 322 may beresiliently inverted prior to insertion of catheter 310 into vessel 340.Alternatively, lobes 322 are inverted when the lobes hit an obstructionin vessel 340. If the obstruction is small, catheter 310 will glide byit. However, if the obstruction is large, lobes 322 and/or cap 320 willbe bent back by the, pressure, such that the resulting streamlined tipwill easily glide past the obstruction. The resilient inversion ofresilient cap member 320 greatly facilitates insertion of catheter 310into vessel 340, and provides a high degree of insertion safety, therebysubstantially eliminating the possibility of catheter 310 scraping aninner surface of vessel 340. Because of radial dimple 330, there issubstantially no build-up or bunching of material in the inverted stateof lobes 322.

Upon proximally directed motion of catheter 310 in vessel 340, resilientcap member 320 once again becomes non-inverted and generally reverts tothe shape illustrated in FIG. 14A. Alternatively, in some embodiment ofthe invention, cap 320 reverts to its previous shape (FIG. 14A) when itis unconstrained by vessel 340, for example, when entering the heart.

It should be noted that when catheter 310 is extracted from the body,lobes 322 form a streamlined shape which does not interfere with theextraction.

Reference is now made to FIG. 16 which illustrates using catheter 310 tosense a physiological activity of tissue inside a body organ, inaccordance with a preferred embodiment of the present invention. In FIG.16, the body organ shown is a heart, but it is appreciated that theinvention may be carried out for any other body organ as well. If themapped organ is the brain, more flexible lobes are preferably used, asbrain tissue is much weaker than vascular tissue and more liable totear.

Catheter 310 is inserted into a body organ, such as a left ventricle ofa heart, typically via the aortic valve. Catheter 310 is inserted sothat sensors 332 contact a tissue, such as the endocardium. Depending onthe type of sensor, it may be sufficient to bring sensor 332 in closeproximity to the tissue without having to actually touch the tissue.Resilient cap member 320 substantially prevents accidentally puncturing,scraping or otherwise damaging inner walls of the left ventricle, byvirtue of its large cross-section. Sensors 332 then sense aphysiological activity of the tissue. Sensors 332 may sense thephysiological activity substantially simultaneously, or alternatively,one at a time. Sensors 332 may sense, for example, a movement of thetissue, contraction time of the myocardium, or an activation signal ofthe myocardium. In this way, the contraction time of the heart musclerelative to the activation signal of the heart muscle, may bedetermined. As a further example, sensors 332 may sense velocity offluid flow in or near the tissue. In a preferred embodiment of theinvention catheter 310 comprises at least four non-coplanar pressuresensors, so that a true three-dimensional pressure gradient may becalculated. Such a pressure may be easily converted into a velocityvector, as known in the art.

In some preferred embodiments of the present invention, the device thatgenerates coordinate information 32 generates six-dimensional positionand orientation information As noted earlier in reference to FIG. 2,device 32 may, for example, comprise a plurality of coils, and asdescribed in PCT patent application number PCT/US95/01103, filed Jan.24, 1995, which is assigned to the assignee of the present applicationand whose disclosure is incorporated herein by reference. Preferredembodiments of this device use a plurality of non-concentric coils, (notshown in the figures), adjacent to a locatable site in catheter 20, forexample near its distal end, or on the structure on which electrodes 26,28, 30 are placed, such as ring 24 or 44. These coils generate signalsin response to externally applied magnetic fields, which allow for thecomputation of six location and orientation coordinates, so that thelocation and orientation of the catheter in the heart are known withoutthe need for simultaneous imaging, by fluoroscopy or ultrasound, forexample. Device 32 generates coordinate information relative to anexternal reference frame defined by electromagnetic field generatorcoils 27, which are fixed to the external reference frame.

Other preferred embodiments of the present invention comprise one ormore devices for generating three-dimensional location information, asdescribed, for example, in U.S. Pat. No. 5,391,199, to Ben-Haim, and PCTpatent application PCT/US94/08352, which are assigned to the assignee ofthe present application and whose disclosures are incorporated herein byreference. One or more devices for generating location information areplaced in the catheter or in the structure containing the electrodes, inproximity to electrodes 26, 28, 30. The respective location informationgenerated by these devices is used to determine the positions of theelectrodes.

In one such preferred embodiment of the present invention, two or moredevices for generating three-dimensional location information are placedin known, mutually-spaced locations in the catheter or in the structurecontaining the electrodes, thereby allowing the positions of theelectrodes in the structure to be determined.

The device disclosed in the aforementioned '539 patent application forgenerating three-dimensional location information preferably comprises asingle coil in catheter 20. In preferred embodiments of the presentinvention that include a device of this type, the coil is toroidal inshape and coaxial with the long, central axis of the catheter. Theseembodiments thus have the advantage that the catheter may have one ormore lumens, which pass through the opening at the center of thetoroidal coil, while maintaining a relatively small external catheterdiameter.

In some preferred embodiments of the present invention, a device thatgenerates three-dimensional location information is placed in thecatheter adjacent to the electrodes and is used to determine thelocation of the catheter inside the heart, while one or more rotationmeasuring devices measure the angular orientation of the catheter. Therotation measuring devices may be of any suitable type known in the art,such as, for example, shaft encoder devices adjacent to the proximal endof the catheter.

For example, in a preferred embodiment of the present invention shown inFIG. 17, a catheter 20 comprises at its distal end a substantially rigidring 24 to which electrodes 26, 28 and 30 are fixed. The catheterfurther comprises a device that generates three-dimensional locationinformation 100, which device preferably comprises a coil coaxial withthe long central axis 45 of catheter 20. A tip deflection device 102, ofa type known in the art, causes the distal end of the catheter to flexfrom side to side within a plane defined by ring 24, under the controlof steering wire 104.

The operator of catheter 20 controls the catheter's movement using ahandle 106 at the catheter's proximal end. Handle 106 includes a firstcontrol knob 108, which is coupled to steering wire 104 via a drum andthereby controls the flexing of tip deflection device 102, and a secondcontrol knob 110, which controls the rotation of the catheter about itslong central axis 45. Shaft encoders 112 and 114 are coupled to knobs108 and 110 respectively, and generate information regarding the tipdeflection and rotation angles of the catheter. Since the positions ofelectrodes 26, 28 and 30 in ring 24 are known relative to the distal endof the catheter, the location information generated by device 100, takentogether with the angles of rotation and deflection of the catheter asdetermined from the information generated by shaft encoders 112 and 114,is sufficient to track the location and orientation of ring 24 in theheart relative to a known starting position. If desired, the startingposition may be verified by fluoroscopy or another imaging techniqueknown in the art.

FIGS. 18A and 18B illustrate a catheter steering mechanism for acatheter 432 in accordance with a preferred embodiment of the invention.The mechanism, indicated by the dotted line, includes a stiffener 420attached to a flat, flexible, elastic, member 416. The distal portion ofmember 416 is coiled into a spiral, through which a loop 430 isthreaded. Loop 430 is formed at a distal end of a pull wire 412, whichwhen pulled, cause flexible member 416 to bend, thereby bending the tipof catheter 432. Since member 416 is flat, it has a preferred bendingplane perpendicular to its face, along arrow 434. The proximal end ofpull wire 412 is preferably wound on a shaft 414, such that when shaft414 is rotated, pull wire 412 is either tensed or relaxed, based on theturn direction. Pull wire 412 is preferably formed of Kevlar.

As is more clearly shown in FIG. 18B, loop 430 surrounds inner wires 428of catheter 423. Wires 428 usually transmit sensor signals to and fromthe sensors and/or electrodes and or position sensors at the distal endof a catheter 432. A plurality of spaces 422 separate member 416 frompull wire 412, so that they do not get tangled together. It should benoted, that since wires 428 fill the bulk of catheter 432, spacers 422may be flexible (but inelastic) and are also preferably formed ofKevlar.

In the preferred embodiment shown in FIG. 2, field generator coils 27fixed to operating table 29 define an external reference frame, relativeto which the position of position information generating device 32 isdetermined. In other preferred embodiments of the present invention,however, an external reference frame is defined and fixed relative tothe heart muscle, as described, for example, by U.S. Pat. No. 5,391,199and U.S. provisional patent application 60/009,769, filed Jan. 11, 1996,which are assigned to the assignee of the present application and whosedisclosures are incorporated herein by reference. These disclosuresteach apparatus and methods for mapping the interior of the heart usingtwo catheters, each of which includes a device that generates coordinateinformation. One of the catheters is positioned in a predetermined,substantially fixed location in the heart, preferably at the apex of theheart, and serves as a reference catheter. By fixing the reference frameto the heart, errors in mapping of the heart that may arise due to themotion of the heart and chest are reduced.

Accordingly, in a preferred embodiment of the present invention, twocatheters are inserted into heart 120. The first catheter 20 comprisesring 24 with electrodes 26, 28, 30 and coordinate information generatingdevice 32 at its distal end, as described above. A second catheter, alsocomprises a coordinate information generating device adjacent to itsdistal end, and is positioned in a predetermined, substantially fixedlocation in a chamber of the heart, preferably at the apex of the heart.This second catheter thus defines a reference frame that issubstantially fixed with respect to the heart, relative to which theposition of the first catheter is determined.

This preferred embodiment has the advantage that errors in mapping thepropagation of electrical impulses in the heart that may arise due tomotion of the heart and chest are avoided, and furthermore thatelectrical propagation vectors, such as activation vector {right arrowover (V)}, may be mapped relative to an accurate map of the interior ofthe heart generated in accordance with U.S. Pat. No. 5,391,199 and U.S.provisional patent application 60/009,769, filed Jan. 11, 1996. Theframe of reference defined by the second catheter also enables theoperator to navigate the first catheter around the interior of the heartwithout the need for simultaneous fluoroscopic or other imaging.

In some preferred embodiments of the present invention, however,ultrasound or X-ray imaging may be used to determine the position of thefirst and/or second catheter in relation to the heart, so as to verifythe reference points of the mapping of propagation of electricalimpulses in the heart. In this case, the catheter to be imaged mustinclude a suitable radio-opaque or ultrasound-reflecting marker.

In other preferred embodiments of the present invention, the fieldgenerator coils that provide the reference frame for coordinateinformation device 32 are fixed externally to the patient's body.Position detection is synchronized with an external electrocardiogramsignal, so that the position is always detected at the same point in theheartbeat, and the influence of the heart's motion on the detectedposition of the catheter is neutralized.

In some such preferred embodiments, movements of the patient's thoraxdue to respiration are also detected, using methods known in the art,such as bio-impedance measurement. Position detection is synchronizedwith the respiration cycle, for example by accepting signals fromcoordinate information device 32 only at and immediately followingmaximum exhalation or only during the tail end of exhalation, so as toeliminate errors in position measurement that may generally arise as theresult of such movements.

While the above preferred embodiments have been described with referenceto measurement of electrophysiological signals in the heart, otherpreferred embodiments of the present invention may be used to measureand map electrical signals in the brain or in other physiologicalstructures.

Furthermore, in other preferred embodiments of the present invention,other sensors, such as ionic sensors, may be used instead of theelectrodes to perform localized measurements and map other aspects ofphysiological activity.

In a preferred embodiment of the present invention, for use indiagnosing and treating defects in the heart's electrical conduction,the distal end of the catheter is placed in proximity to the suspectedsite of a defect. On the basis of the vector direction and magnitude ofthe electrical propagation vector measurer at this initial site, thecatheter is then moved toward the suspected defect site. This procedureis repeated until the catheter reaches the actual site of the defect.Preferably, once the defect is located by the above procedure, it isablated or otherwise treated by methods known in the art. It should beappreciated, that this procedure may be performed even without referenceto a reference frame outside of the catheter.

In some preferred embodiments of the present invention, arrhythmias andpathological cardiac events arc detected, using methods known in theart, simultaneously with determining the velocity vectors in accordancewith the method described above. Each velocity vector is classified andstored, preferably by computer 51 or other electronic data storagedevice, according to a type of cardiac arrhythmia or event (or normalheart beat) that occurred at the time the electrogram signals used todetermine the vector were received. Stored vectors that have beenclassified as belonging to a specific arrhythmia or event are then usedto generate a map of the propagation of electrical activation in theheart that is characteristic of that arrhythmia or event. Such maps maybe useful, for example, in detecting abnormal propagation of theactivation front that is associated with a specific arrhythmia,including cases in which multiple activation fronts pass a location inthe heart during a single R—R cardiac cycle interval.

It will be appreciated that the preferred embodiments described aboveare cited by way of example, and the full scope of the invention islimited only by the claims.

What is claimed is:
 1. A catheter for measuring physiological signals ina heart, the catheter comprising: a structure at a distal end of thecatheter, the structure having: (i) a plurality of arms; (ii) anelectrode fixed to each arm, and (iii) a device for generating positioninformation located on each arm, wherein the arms are located near along axis of the catheter during insertion of the catheter within aheart and the arms are spreadable apart and away from the long axis ofthe catheter when the structure is within the heart.
 2. The catheteraccording to claim 1, wherein the device for generating positioninformation is a position sensor.
 3. The catheter according to claim 2,wherein the position sensor generates signals responsive to anexternally-applied field.
 4. The catheter according to claim 3, whereinthe externally-applied field is a magnetic field.
 5. The catheteraccording to claim 2, wherein the position sensor comprises at least onecoil.
 6. The catheter according to claim 5, wherein the at least onecoil is used for determining position and orientation information. 7.The catheter according to claim 2, wherein the catheter is used tomeasure electrical activation in the heart.
 8. The catheter according toclaim 7, wherein the catheter is used to map electrical activation inthe heart.